Field of the Invention
The present invention relates to a method for manufacturing a magnetic recording medium.
Description of the Related Art
A perpendicular magnetic recording system has been adopted as a technology for increasing the recording density of a magnetic recording medium. A medium recorded magnetically by this system (a perpendicular magnetic recording medium) has a nonmagnetic substrate formed from a nonmagnetic material, an underlayer, a magnetic recording layer, a protective layer for protecting the surface of the magnetic recording layer, and a liquid lubricant layer. The medium sometimes further has a soft magnetic under layer that is formed from a soft magnetic material and plays the role of concentrating a magnetic flux generated by a magnetic head onto the magnetic recording layer.
As a magnetic recording layer of a perpendicular magnetic recording medium, there is proposed a magnetic recording layer having a granular structure in which a nonmagnetic substance such as SiO2 or TiO2 is added to an alloy material such as CoCrPt or CoCrTa (granular magnetic recording layer) (Japanese Patent Application Publication No. 2001-291230). In a CoCrPt—SiO2 granular magnetic recording layer, for example, a SiO2 nonmagnetic substance is segregated around CoCrPt magnetic crystal grain and separates the individual CoCrPt magnetic crystal grain magnetically. In addition, a stacked body with a plurality of magnetic recording layers or an exchange-coupled composite (ECC) structure having an exchange-coupling control layer inserted between magnetic recording layers, is used in the perpendicular magnetic recording medium. Stacking a plurality of magnetic recording layers provides the effect of reducing magnetic switching loss while ensuring thermal stability. Note that each of the magnetic recording layers here is a single layer. Furthermore, in recent years, for the purpose of making up for a reduction in thermal stability, L10-ordered alloy (Strukturbericht designation) such as CoPt or FePt has been proposed as a material with higher magnetocrystalline anisotropy (Ku) (Japanese Patent Publication No. 3318204). An underlayer plays an important role in formation of a L10-ordered alloy layer. This is because crystals of L10-ordered alloy need to have a (001) orientation (a [001] axis of each crystal is positioned perpendicularly to a film surface) in order to provide magnetic crystal grain with a high magnetocrystalline anisotropy. In so doing, MgO having high lattice matching with the L10-ordered alloy is generally used as the underlayer.
In this manner, granular structure control, exchange-coupling control between magnetic recording layers, crystalline orientation control with lattice matching using an underlayer, and other advanced control are performed on each magnetic recording layer in order to improve the performance of the magnetic recording medium, requiring further improvement of the quality of each magnetic recording layer.
A magnetic recording layer is generally formed using a vacuum deposition equipment such as a sputtering/deposition/CVD equipment. It is effective to remove, as much as possible, impurity gas such as H2O, O2, H2, CO, CO2 and the like remaining in a vacuum in order to further improve the quality of the generated magnetic recording layer. Among the conventional semiconductors, there is proposed a getter pump for absorbing impurity gas inside a vacuum chamber of a vacuum deposition equipment by using an active material such as Ti to improve the quality of a generated film. The getter pump heats and thereby evaporates a filament made of an active material, to generate a clean active material film on an inner wall of a chamber, and then absorbs and removes impurity gas such as H2O, O2, H2, CO, CO2 and the like remaining in a vacuum, by means of the active material film. As a vacuum processing equipment capable of absorbing/removing impurity gas by using an active material with no spatial constraint of a vacuum chamber caused by a getter pump, there is proposed a vacuum processing equipment that has a shield plate and provides an opposite surface of a processing part of the shield plate with an absorption film of an active material for absorbing impurity gas (Japanese Patent Application Publication No. 2001-234326). There is also proposed an equipment in which a target is configured by a film-forming material region and an annular active material surrounding the film-forming material region and a shield is used to block sputtered particles generated from an active material region (Japanese Patent Application Publication No. 2010-106290).
However, one of the major problems of the technology using a conventional getter pump is a spatial constraint in the vacuum chamber. Another problem is a worsening of the magnetic property of the magnetic recording medium due to an accumulation of the heated/evaporated active material on the medium substrate.
Moreover, in the method for preventing the active material from accumulating on the substrate by blocking the active material with the shield, the shield often needs to be replaced because particles are produced as a result of an accumulation of the active material on the shield, deteriorating the maintenance and productivity.
In addition, in the invention disclosed in Japanese Patent Application Publication No. 2010-106290 in which the target is configured by the film-forming material region and the active material surrounding the film-forming material region and the shield is used to block the sputtered particles generated from the active material region, it is difficult to create the target, and the maintenance becomes worse.